System-on-chips, in operation, emit electromagnetic radiation. This electromagnetic emission (EME) can be caused by switching of logic gates. Electromagnetic emissions are typically undesirable. Given a draft design of the system, the draft design may be improved by reducing electromagnetic emission. To this end, an iterative design process can comprise that operation of the draft design is simulated to determine the electromagnetic emission and the draft design is then amended with a view to a reduction of the emission. The simulation requires the draft design to be completed before it can be simulated, even though for improvement of the design, vast amendments may eventually provide for a very different design. The simulation is complex to perform commensurate with the complexity of the draft design.